1. Field of the Invention
The present invention generally relates to the field of Geographic Information Systems (GIS), and more specifically to a method for automatically displaying map symbols in accordance with the current map scale and symbol overlap.
2. Description of the Related Art
A typical GIS uses a computer to access records from a data base to display maps and map symbology on a display screen. The records contain the spatial and descriptive information associated with the features found in a map. The features are represented graphically as points, lines and areas. The records for point features also include a descriptive symbol of the feature. The graphical representation of these features, including the point feature symbols, are displayed on the computer screen.
In a military application, point features such as troop units, planes, and artillery pieces are added to the normal geographic features such as roads, waterways, and buildings, and superimposed over the geographic map on the display screen. An analyst might view the map display to determine troop strength and position. The analyst interacts with the GIS to zoom in or out on the map to display a desired portion or scale of the map. The features lying within the selected portion of the map are displayed as point symbols, lines or areas. It is very important that the map display clearly and accurately depict the map features at all map scales and for all regions of the map.
This method of displaying map symbology has a number of drawbacks. First, if the displayed portion of the map is densely populated with map symbols the display can be cluttered with overlapping symbols. Furthermore, as the analyst zooms out to display a larger portion of the map, additional symbols are displayed on the screen in closer proximity, thus increasing the clutter due to symbol overlap. Additionally, the degree of symbol clutter may vary throughout the display depending on the symbol overlap in local regions of the map. The symbol clutter detracts from the analyst's ability to accurately evaluate the visual display.
Currently, the only option available to the analyst is to zoom-in until the symbol clutter decreases to an acceptable level. Although the resolution of the map display can change, the resolution of the map symbology is fixed. This inhibits the analyst's ability to view large scale regions of the map and, if it is desired to differentiate the symbols, requires a great amount of the analyst's time to zoom-in on each portion of the entire region to gather the necessary information. The current method for displaying map symbology fails to effectively resolve the problem of clutter due to symbol overlap.